# -*- coding:utf-8 -*-
# @Time: 2020/9/16 20:36
# @Author: 周铖鑫
# @Description：annotation的使用
# @File: UseAnnotation.py
import  matplotlib.pyplot as plt
import numpy as np
x=np.linspace(-3,3,50)
y=x*2+1

plt.figure(num=1,figsize=(8,5))
#放置两条线
plt.plot(x,y)
ax=plt.gca()
#spines上下左右边框
ax.spines['right'].set_color('none')
ax.spines['top'].set_color('none')
ax.xaxis.set_ticks_position('bottom')
ax.yaxis.set_ticks_position('left')
ax.spines['bottom'].set_position(('data',0))
ax.spines['left'].set_position(('data',0))

x0=1
y0=2*x0+1
#scatter画出来的是离散的点(散点图）
plt.scatter(x0,y0,s=50,c='green')
plt.plot([x0,x0],[y0,0],'k--',lw=2.5)
#method 1
#########
#xytext相对于点的位置+-
plt.annotate(r'$2x+1=%s$'%y0,xy=(x0,y0),xycoords='data',xytext=(+30,-30),textcoords='offset points',
             fontsize=16,arrowprops=dict(arrowstyle='->',connectionstyle='arc3,rad=.2'))

#method2
plt.text(-3.7,3,r'$This\ is\ some\ text.\ mu\ \sigma_i\ \alpha_t$',fontdict={'size':16,'color':'r'})
plt.show()